1. Field of the Invention
The present invention relates to a semiconductor light-emitting device and, more particularly, to a semiconductor light-emitting device with an enhanced external quantum efficiency and a good epitaxy quality.
2. Description of the Prior Art
The current semiconductor light-emitting devices, such as light-emitting diodes, have been used for a wide variety of applications, e.g. illuminations and remote controls. To ensure high functional reliability as great as possible and a low power requirement of the semiconductor light-emitting devices, the external quantum efficiency is required for the devices.
In principle, the external quantum efficiency of a semiconductor light-emitting device is determined both by the internal quantum efficiency and extraction efficiency. The internal quantum efficiency is determined by the material property and quality. The extraction efficiency refers to the proportion of radiation emitted from the interior of the device into the surrounding air or encapsulating epoxy. The extraction efficiency is determined by the losses occurred when radiation leaves the interior of the device. One of the main causes for such losses is the high refractive index of the semiconductor material so the radiation cannot be emitted outside at the semiconductor surface on account of total reflection.
Please refer to FIG. 1. To enhance the external quantum efficiency of the semiconductor light-emitting device, a sapphire substrate 1 with a patterned surface 10 has been disclosed and applied to the manufacture of the semiconductor light-emitting device. FIG. 1 illustrates a schematic view of a conventional sapphire substrate 1 with a patterned surface 10. The patterned surface 10 is for scattering light emitted out from the semiconductor light-emitting device to reduce the probability of a total reflection, and further to enhance the external quantum efficiency of the semiconductor light-emitting device.
Although a semiconductor material layer, e.g. a GaN layer, can be formed on the patterned surface 10 of the sapphire substrate 1 through a good lateral epitaxial growth, the GaN layer can not be grown on the patterned surface 10 of the sapphire substrate 1 directly, i.e. a poor vertical epitaxial growth. Therefore, the quality of the GaN semiconductor material layer formed on the patterned surface 10 of the sapphire substrate 1 is still required for improvement.
Inside the semiconductor light-emitting device of the prior art, a buffer layer can be formed between a semiconductor material layer and an ordinary substrate to improve the quality of the semiconductor material layer. As a result, the external quantum efficiency of the semiconductor light-emitting device will further be enhanced by the buffer layer.
Accordingly, the main scope of the invention is to provide a semiconductor light-emitting device with an enhanced external quantum efficiency and a good epitaxy quality.